Remove the use of type_index with unordered_map for components. Even though unordered_map has an amortized constant lookup/insertion time, it's still a few orders of magnitude slower than a raw vector.

Since components won't need to be un-registered, implement a "family ID" setup for Component types that starts at 0. Then, use a vector where the index is the ID, in these situations:

• In the ComponentPool, to store multiple ComponentArray instances
• In EntityData (inside of Core) to store the component set for each Entity
  • The component set should be resized to the total number of component types, so adding new components won't trigger reallocations.
  • While the component sets are going to be initially larger, they will still be relatively small. It's worth it for the performance improvement and consistency. Even unordered_map takes up extra memory than the number of elements inside it anyway.